LA risks Flashcards
State some instances which may lead to unwanted effects of LA administration
- injecting an inappropriate solution
- injecting too much solution
- injecting wrong site
- bad luck
What are the most serious adverse effects of LA administration
- CNS problems as a result of overdose or intra-arterial injection
- long standing nerve problems after regional block anaesthesia
What is the only absolute contraindication of the use of LA?
allergy to the solution
What type of LA more commonly gives rise to an allergic reaction?
Ester anaesthetics
What ester local anaesthetics are used as topical agents ?
- benzocaine
- amethocaine
What agent is commonly implicated in an allergic reaction during the delivery of local anaesthetic?
latex
which is used in the manufacture of some cartridges
Give examples of latex free cartridges of LA
- Septanest (articaine +adrenaline)
- Citanest (prilocaine with octapressin)
What should you do if a patients presents with a history that may predispose them to an allergic reaction to LA/LA components?
- referral for allergy testing
- establish a suitable alternative drug
Briefly explain the mechanism of reverse carotid flow
- injection under strong pressure into a branch of the external carotid artery can cause some LA solution to flow into carotid bifurcation (solution travels against the arterial flow to reach the bifurcation)
- a portion can then be redirected to the brain via the internal carotid artery
If patient reports tachycardia following LA delivery, how can you manage this in the future?
avoid the use of adrenaline containing solution
State a guideline for detemining the maximum dose of local anaesthesia
1/10th of a cartridge per kilogram
What organ suffers during LA overdose? Why is this
- the brain
- this is because CNS tissue is more susceptible to the actions of LA than peripheral sensory nerves
What are the first signs of LA toxicity?
excitability as the inhibitory actions of the brain are the first to be depressed
What are the later signs of LA toxicity?
- CNS depression; this can lead to unconsciousness
- death due to respiratory depression
Why is it not possible to change to another LA after the maximum dose of one has been administered?
this is because the effects of LA are cumulative
What are the injection sites for LA that cause problems?
- intra-arterial
- intravenous
- intraneural
What problematic site of injection has a higher incidence?
intravenous
- more common than intra-arterial
What is the main consequence of intra-arterial injections?
- LA solution is delivered directly into the CNS
- interference with special senses e.g.:
- sight- double vision as orbital muscles can be affected
What is the cause of permanent loss of sight following intra-arterial LA delivery?
- occlusion of retinal artery
- introduction of emboli into the opthalmic artery
Hearing loss following LA may occur as a result of…
- CNS toxicity
- ischaemia of the cochlea following intravascular injection
What is the most severe consequence of intra-arterial LA delivery? What is the cause of this?
hemiparesis of the body
result of reverse carotid flow of LA
What is the danger of intravenous LA delivery ?
- production of systemic effects such as CNS toxicity, heart effects e.g. tachycardia and arrhythmias
Damage to the nerve trunk following intraneural injection can be classified as…
- physical- needle trauma
- chemical- dispersal of solution into nerve bundle
What are the consequences of intra-neural injection ?
- long term anaesthesia - lack of sensation
- parasthesia- altered sensation e.g. pins and needles
- dysaesthesia (pain)
Dysaesthesia is more likely following LA than surgery. True or false
true
What is the consequence of penetrating both sides of a blood vessel?
bleeding
What is the consequence of LA induced bleeding on the medial pterygoid muscle?
trismus
What is the best way to avoid injecting into a blood vessel?
use of an aspirating syringe system
State an instance where aspiration of a syringe can fail
aspiration may fail if the needle is blocked by the wall of the blood vessel
aspiration will occur when the tip of the needle is in the blood vessel
Aspiration may be impeded by vessel wall obstruction. How do you manage this?
slow injection to prevent retrograde flow of solution
slow injection helps to reduce damage to the nerve
Suggest the best way to prevent nerve injury
avoid regional block injections
If an “electric shock” type reaction is noted on the delivery of the IANB, what should you do ?
no solution should be injected at that point
needle should be moved a few mm away before injecting
Intraneural injection always produces pain and causes nerve injury. True or false
False
Around __% of IANB produces an electric shock type sensation. What is the consequence of this type of sensation ?
8%
around 15% of people who experience this sensation experience long-lasting altered sensation of a varied duration
__% of patients who suffer from prolonged altered sensation did not experience an “electric shock” at the time of injection
57%
In what instances does LA delivery cause nerve damage?
when LA is injected under pressure
What are the advantages of injecting slowly ?
- less patient discomfort during infiltrations and regional block injections
- increased efficacy of IANBs
- reduction of systemic adverse effects
- minimise possibility of reverse carotid flow
What is the recommended rate of LA delivery?
30 seconds per ml of solution
The higher the concentration of LA, the ________ the nerve cell survival
lower
reports that nerve damage is more common after the use of 4% compared to 2% solutions
What nerve is most commonly damaged following IANB?
lingual nerve
accounts for 70% of the damage
Give some reasons why the lingual nerve is more likely to suffer damage
- over-reporting of such injuries happens with new drug formulations such as articaine
- at the region of the lingula, the lingual nerve is composed of very few fascicles and in some individuals it is unifascicular at this point
- this is unlike the IAN which is multi-fascicular at the region of the lingula
this structural difference may account for increased susceptibility of the lingual nerve
What LA has been shown to be more effective than 2% lidocaine for mandibular infiltrations?
4% articaine
There is strong evidence to suggest that 4% articaine is more effective for IANBs compared to 2% lidocaine. True or false
False
hence there is no advantage to using it for the IANB
State alternatives to regional block techniques
- intraligamentary
- intraosseous
What complications are associated with intraligamentary/intraosseous injections ?
damage to periodontium
Briefly state preventative measures for preventing risks associated with LA
- good medical history
- aspirating syringe
- limit use of regional block injections
- inject slowly
What is the maximum dose of 2% lidocaine (mg/kg)?
4.4
What is the maximum dose of 2% mepivacaine (mg/kg)
4.4
What is the maximum dose of 3% mepivacaine (mg/kg)
4.4
What is the maximum dose of 3% prilocaine (mg/kg)
6.0
What is the maximum dose of 4% prilocaine (mg/kg)
6.0
What is the maximum dose of 4% articaine (mg/kg)
7.0
